Java tutorial
/* * Copyright 2013 - 2018 Anton Tananaev (anton@traccar.org) * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.traccar.protocol; import io.netty.buffer.ByteBuf; import io.netty.channel.Channel; import io.netty.channel.ChannelHandlerContext; import java.nio.charset.StandardCharsets; import org.traccar.BaseFrameDecoder; import org.traccar.helper.BufferUtil; public class TotemFrameDecoder extends BaseFrameDecoder { @Override protected Object decode(ChannelHandlerContext ctx, Channel channel, ByteBuf buf) throws Exception { if (buf.readableBytes() < 10) { return null; } int beginIndex = BufferUtil.indexOf("$$", buf); if (beginIndex == -1) { return null; } else if (beginIndex > buf.readerIndex()) { buf.readerIndex(beginIndex); } int length; if (buf.getByte(buf.readerIndex() + 2) == (byte) '0') { length = Integer.parseInt(buf.toString(buf.readerIndex() + 2, 4, StandardCharsets.US_ASCII)); } else { length = Integer.parseInt(buf.toString(buf.readerIndex() + 2, 2, StandardCharsets.US_ASCII), 16); } if (length <= buf.readableBytes()) { return buf.readRetainedSlice(length); } return null; } }